Automationdirect.com HX-ECOM Series - The Second LD Instruction; The LDA Instruction

Ethernet Communications Modules, 3rd Edition, Rev. D
4–4
Chapter 4: RLL Programming for Communications
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The Second LD Instruction
The second Load (LD) instruction determines the length of
the data block to be transmitted during the Read or Write
communication. This instruction will also accept two data
types. Use a “K” to designate the number as a constant. Use a
“V” if you are entering the address of a register.
For Word Memory data, you must use a multiple of two
bytes between 2 and 128. For Bit Memory data, you can
use any multiple of one byte between 1 and 128. For more
information about addressing Word and Bit Memory, see page 4-6.
The LDA Instruction
The Load Address (LDA) instruction specifies the V-memory
address of the beginning memory register in the initiating,
or master, PLC. The data block to be transmitted will begin
at this address and extend the number of bytes specified in
the preceding LD instruction. The leading “O” indicates this
is an octal number. Simply substitute the letter “O” for the
“V” in the V-memory designation. For example, V40600
becomes O40600.
Read instructions copy the data block from the responding
PLC memory into the initiating PLC memory.
Write instructions copy the data block from the initiating
PLC memory into the responding PLC memory.
PLCMemory
V40600
V40601
V40602
V40603
V40577
V40604
InitiatingPLC
PLCMemory
V40600
V40601
V40602
V40603
V40577
V40604
InitiatingPLC
LD
K114
LD
K8
4 words = 8 bytes
LD
K114
LD
K8
LDA
O40600